Catalytic combustion devices are employed in a variety of applications. A typical application involves the use of the catalytic combustion device to combust left over fuels that are contained within effluents exhausted from a power system within which the catalytic combustion device is employed. The power systems within which the present invention can be employed use a fuel source, such as hydrogen (H2) and an oxidant source, such as oxygen (O2) and/or air (O2 admixed with nitrogen (N2)) to produce electrical power. The creation of electrical power within the power system results in effluents that are exhausted from the power system. The effluents typically contain unused fuel in the form of H2 and unused oxidant in the form of O2 and/or air. These effluents represent a source of energy that can be used. To extract the energy from the effluents, these power systems typically employ a catalytic combustion device that combusts the unused H2 contained within the effluent to produce heat that can be used within the power system to meet a heat demand.
The amount of H2 contained within the effluent will vary depending upon the efficiency of the power system and the conditions under which the power system is operated. Because the amount of H2 contained within the effluent varies, the catalytic combustion device typically includes a liquid fuel supply that can be used to increase the amount of combustible fuel within the combustion device so that heat demands placed on the combustion device by the power system can be met. Additionally, because the amount of H2 contained within the effluent varies, the amount of reaction occurring in any particular area within the combustion device can also vary and result in hot spots or locations of excessive heat that can damage the combustion device. The effluents and any liquid fuel flowing into the combustion device are a flammable fuel mixture. The temperature at which the fuel mixture will autoignite will vary depending upon the composition of the fuel mixture.
Conventional combustion devices are designed to preclude autoignition of the fuel mixture. When autoignition of the fuel mixture within some areas occurs, the combustion device typically is damaged and possibly completely destroyed. In one solution to the autoignition concern, the fuel mixture is passed through a high density foam structure, prior to entering the area of the combustion device where the catalytic reaction is occurring and excessive heat build up can occur. The high density foam structure induces mixing as well as producing a high velocity exit gas. As long as the velocity of the combustible fuel mixture exiting the high density foam structure is greater than the fuel mixture flame speed and the material is below the autoignition temperature, the fuel mixture upstream of the high density foam structure will not ignite. That is, the high density foam structure acts as a flame arrestor and prevents flame propagation across the high density foam structure.
While the use of the high density foam structure may prevent flame propagation to an undesirable area in the combustion device, the high density foam structure produces a significant pressure drop as the fuel mixture flows through the high density foam structure. The pressure drop is undesirable because it may require the effluents flowing into the combustion device to pass through additional equipment to increase the pressure of the effluents prior to entering the combustion device so that adequate pressure and flow of the effluents through the combustion device is achieved. The extra equipment to pressurize the fuel flow increases the complexity and cost of the system within which the combustion device is employed.
Therefore, it would be desirable to provide a combustion device that does not require the use of a flame arrestor or reduces the density of the flame arrestor so that the pressure drop across the flame arrestor is smaller and does not require the effluents to flow through any additional equipment prior to entering the combustion device. Additionally, it would be desirable to provide a combustion device that can utilize a liquid fuel injection system to provide a fuel to the combustion device so that the combustion device can meet a heat demand of the power system during the start up operation of the power system where the amount of effluent being exhausted by the power system may not be sufficient to meet the heat demand of the power system.